1. Field of the Invention
This invention generally relates to an abnormality-detecting device for use in a brake system of an automotive vehicle. More particularly, it relates to a device for continuously or intermittently detecting thickness displacement of the frictional braking element or lining of the brake shoe by detecting said displacement as coil inductance variation through a pick-up coil secured to the brake shoe, and also for detecting a critical temperature rise in the brake system by converting temperature changes into electrical signal potential changes through the same coil.
2. Description of the Prior Art
In general, for measurements of spatial distance (gap) or length there have been known various devices such as mechanical measurement devices, electrical measurement devices or optical measurement devices, etc. For the ordinary measurements, these measuring systems of the prior art are satisfactory in use and performance.
However, these conventional measuring devices are usually arranged separately from or independently of the object to be measured, and only when the measurement is made, the device is temporarily applied to the object to be measured, or the object to be measured is applied to the device. The reasons for the necessity of such arrangement are primarily that the conventional measuring devices are generally of complex structure, the devices themselves are of large-size, and still more they tend to be subject to external disturbances such as undesirable vibrations and the like that may cause a lowering of the measuring accuracy.
Accordingly, with the measuring devices of the prior art, there has been encountered such a difficulty that when an object to be measured is incorporated in machinery, for example, as its component part, it takes many hours, with the machinery being inconveniently held out of operation, to complete measuring the distance (or gap) or length in connection with the object. A further drawback has been that during the running of machinery, it is not possible to detect the rate or type of changes occurring in the distance or length. Particularly, it has been extremely difficult to detect the distance or length between moving members.
In various kinds of machinery or equipment, it is frequently necessitated during the operation to carry out measurements of an object or objects with respect to the distance or length, whether such object constitutes machinery itself or a component part incorporated therein. One example is the measurement of the amount of wear of the lining element in an automotive vehicle brake system.
As well known, the automobile brake system is mounted in the wheel tire, and generally is of the drum-type or disk type. It is commonly so arranged, in either type, that the braking action be effected by exertion of a frictional force produced by pressing the brake lining element secured on the shoe against the brake drum. In view of assuring a safe drive by car, the brake system imperatively needs to provide a consistently satisfactory quality of braking effect. Though there are various factors causing deterioration of the braking effect, the primary one resides in wear of the brake lining due to long use of the brake system. Therefore, the detection of the amount of wear in the brake lining whenever desired is essentially necessary for assurance of a safe drive by car. However, with the conventional brake system mounted in the wheel, it has been extremely hard to detect the amount of wear in the brake lining element. The common practice has hitherto been that on the occasion of overhauling the automobile, the wheel tire assemblies are dismantled, and then the amount of wear in the lining element is measured. This requires much time and labor. Therefore, the ordinary brake system has a serious defect in that during the normal driving conditions of the automobile it is not possible to detect the wear of the brake lining.
There has been known the conventional device in that a sensor means such as a micro-switch or the like is operatively associated with piston means for actuating the brake shoe so that an alarm signal is generated when the amount of wear of the lining reaches a predetermined limit. Nevertheless, this device also involves a fault in that only a critical amount of wear can be detected and there is no sensing or knowing the presently effective thickness of the brake lining whenever desired, and its construction being rather complicated.